RF-excited waveguide, carbon dioxide lasers have found a large number of applications in the last several years because of their compact size, reliability and relative ease of manufacture. The basic patent governing these layers is U.S. Pat. No. 4,169,251, issued to Katherine D. Laakmann. This patent describes the basic geometry and physics of the device. An additional patent, U.S. Pat. No. 4,393,506, issued to Peter Laakmann et al., covers the preferred implementation of such lasers as well as a novel water vapor getter. U.S. Pat. No. 4,373,202, issued to Katherine D. Laakmann et al., covers a longitudinally RF-excited structure.
For commercial purposes and power levels up to about 25 watts, the metal/ceramic technology disclosed in U.S. Pat. No. 4,393,506 has been extremely successful because it combines low manufacturing cost with adequate performance and proven lifetime, measured in years, without gas replacement.
For military purposes, ceramic-only structures are being used to eliminate differential thermal expansion between the ceramic and metal parts of the cavity. The elimination of thermal mismatch is a requirement in these applications because of the typically required operating temperature range of -40.degree. to +50.degree. C. for military hardware. Similarly, high-powered (above 25 watts), folded lasers for commercial applications are also being built from all-ceramic structures to assure the greater precision required by these folded structures. The basic cavity structure of a longitudinally excited, all-ceramic laser is shown in U.S. Pat. No. 4,373,202. The same physical structure has also been used with transverse RF excitation.
The all-ceramic laser is intrinsically more costly to fabricate than the basic commercial metal/ceramic structure. However, for high power output of large operating temperature range, there has so far been no alternative.
An additional problem with both approaches is the fact that assembly and closure involve solder sealing. In the case of the metal/ceramic structure, relatively low-temperature solder sealing must be used to avoid thermal distortion of the composite waveguide. In the case of the ceramic structure, no other method is known to seal the materials. The solder process requires a "wet" wash afterwards, which leads to long reprocessing times to remove water contamination, the enemy of carbon dioxide laser gain.
Another problem in these prior art lasers is that the devices are difficult to "outgas" because the structures involve members under compression trapping gases, particularly water vapor.